Two chemical compounds, P and Q are mixed together in a beaker. State which observation or measurements will show that a chemical change has taken place.
Answers
Here are the five signs of chemical change.
1. Color Change
You've probably seen this kind of chemical change before if you have left your shiny blue bike outside over the rainy winter for too long. You saw rust, of course. Rust forms on your bike when the iron in the metal frame reacts with the oxygen and water in the air. It forms a new compound called iron oxide. This change in color, from blue to reddish brown, indicates that a chemical change has taken place.
2. Temperature Change
When energy is either absorbed or released, it is indicative of a chemical change. Fireworks are an example of a chemical change that produces a temperature change and emits light. Fireworks contain fuel and an oxidizing agent. As the oxidizer breaks down the fuel, it releases an enormous amount of energy. Some of this energy is released as heat, so remember to not get too close!
3. Precipitate Formation
When two salts are mixed, it is possible for a solid substance to form and precipitate out of solution. This means that if you start with two liquids and then see a solid substance in your beaker, it is clear evidence of a chemical change.
Precipitation reactions are very important in making sure water is safe for human consumption. Water purification facilities make use of the fact that they can add a chemical to the water which will react with an impurity in the water and precipitate. Then the now-pure water can be removed from the solid which contains the impurities.
4. Gas Production
Production of gas is a clear sign that a chemical change has occurred. A quite delicious example of that is baking a cake. When you bite into a moist cake and see the tiny holes in the cake, this is indicative of the rising agent (either baking soda or baking powder) reacting with the acidic components of the cake to create carbon dioxide. This gas is what helps a cake rise in the oven.
Make sure you keep in mind what a chemical change really is when looking at different chemical states.
5. Light Emission
There are many reactions that produce light and allow you to see that a chemical reaction has taken place. One example that you may have even witnessed firsthand is the reaction in a light stick. When you bend the light stick and break the small glass vial on the inside you initiate a reaction between hydrogen peroxide and phenyl oxalate ester, which results in the emission of light.
There can be the following observations that would show a chemical reaction taking place:
- Temperature: A change in the temperature shows a chemical reaction has taken place because there is either some kind of absorption of energy or release of energy in order to break or make the bonds between the molecules. These reactions are characterized into two categories namely, exothermic reaction ( in which energy is released) and endothermic reaction (in which the energy is absorbed).
- Color change: The color change is a common phenomenon indicating a chemical reaction taking place because there would be some changes in the properties of the substance and thus the formation of the new properties.
- Formation of gases: One of the most common indicators of reaction taking place is the formation of gases. There is some pop sound or the formation of bubbles after the reaction to show the formation of gas.
- Precipitation: Precipitation is also a sign of reaction taking place. These solids are mainly formed due to the strong attraction force between the ions that come together.
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